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In situ measurements of the porosity on thin oxide films by IR emission spectrometry
Author(s) -
Pigeat P.,
Pacia N.,
Weber B.
Publication year - 1992
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.740180720
Subject(s) - porosity , oxide , tungsten , materials science , tetragonal crystal system , emissivity , porous medium , scanning electron microscope , analytical chemistry (journal) , radiative transfer , particle (ecology) , phase (matter) , mineralogy , chemistry , optics , composite material , physics , metallurgy , oceanography , organic chemistry , chromatography , geology
Observation of the normal spectral emissivity is used as a method of in situ surface investigation. This technique has been used here to follow tungsten oxidation during reactions performed under 1.3 Pa of oxygen both above and below the temperature of the phase transition: ortho‐rhombic αWO 3 → tetragonal α′WO 3 . We show that the difference between the observed radiative behaviour is due to the difference between the morphology of these oxides (αWO 3 is homogeneous and α'WO 3 is porous). From this difference, with an optical model using an effective medium theory (Bruggeman equation), we show that it is possible to describe correctly the experimental measures and to calculate the value of the porosity of the film during its growth. In this model, we show that the best value of the depolarization factor for the oxide particles is 1/3. This is precisely the value that characterizes a porous deposit where the particles (here, oxide particles) are spherical; it is also a good approximation for particles deprived of a particular shape (geometrically isotropic) and disposed at random, such as what we have effectively observed by scanning electron microscopy.